Fast Microwave-Induced Thermoacoustic Imaging And Its Applications

As we all know,our country has made great strides towards an aging society,and medical security has become a vital part of daily life.Among them,biomedical imaging technology,as a visual disease detection method,can collect and visualize the anatomical and functional information of human tissue in a relatively short period,which can assist doctors to make a more accurate diagnosis of patients' symptoms.At present,the main clinical medical imaging techniques,including X-ray,CT imaging,Doppler ultrasound imaging,and magnetic resonance imaging,have certain limitations due to their respective imaging mechanisms.In recent years,the vigorous development of microwave-induced thermoacoustic imaging technology has attracted more and more attention in the biomedical imaging field.It is a new non-invasive,non-ionizing,and real-time biomedical imaging technology.It inherits multiple advantages of high contrast of microwave imaging and high temporal and spatial resolution of ultrasound imaging,and its endogenous contrast is derived from the difference of specific absorption rate of microwave energy in biological tissues.It has been able to complete the detection of a variety of small animal disease models and is stepping up the pace of human tissue and human disease model detection research.To achieve the goal of gradually transitioning microwave-induced thermoacoustic imaging technology from laboratory to preclinical research,it is necessary to greatly improve the time resolution to reduce the influence of dynamic factors such as breathing artifacts and minimize the spatial volume and weight of the imaging system to facilitate clinical portable use.Under such research needs,this dissertation developed a multichannel fast microwave-induced thermoacoustic imaging system that can be applied to the clinical detection of human tissue.Based on the existing microwave-induced thermoacoustic imaging system in the laboratory,the author uses an optimized miniaturized S-band microwave source,and the selection of ultrasonic transducers transitions from the initial flexible array to the linear array,and finally to the self-designed hollow concave array.Combined with a multi-channel fast data acquisition system,a compact and portable fast microwave-induced thermoacoustic imaging system that can be applied in preclinical research on human disease models is designed and built.In addition to designing and building this fast microwave-induced thermoacoustic imaging system,the author also designs and builds a dual-modal ultrasound /thermoacoustic imaging system based on the self-designed concave array and cooperating with the linear array and S-band miniaturized microwave generator.Using these systems,thermoacoustic imaging experiments were carried out on human tissues such as thyroid,blood hematocrit,wrist,and foot in vivo,and the results confirmed the feasibility and good imaging performance of these imaging systems.The author also extended the study on the various characteristics of dielectric properties of 10 in vitro rat tissues in a wide frequency range under the modulation of low-density focused ultrasound field,laying a foundation for subsequent related research and extension to the field of microwaveinduced thermoacoustic imaging.The innovations of this dissertation can be summarized as follows:1.Designed and built a compact,real-time imaging fast microwave-induced thermoacoustic imaging system based on a flexible array,linear array,and hollow concave array separately.It can achieve high-resolution and rapid imaging and detection of the human thyroid,wrists,feet,blood vessels,and other tissues.2.Using a fast microwave thermoacoustic imaging system based on a flexible array ultrasound transducer and a 3.0 GHz microwave source,with a coupling bracket designed independently for the structure of the human neck and supporting the flexible array,highresolution thermoacoustic imaging of in vivo healthy human thyroid gland was achieved for the first time.And the thermoacoustic imaging and monitoring of hematocrit value changes in human arm tissue were realized for the first time,by using the fast microwave thermoacoustic imaging system based on the linear array.3.Independently designed and developed a hollow concave array ultrasonic transducer with high resolution and a large imaging field of view.Based on this concave array and with the linear array and S-band small microwave source,an ultrasound/thermoacoustic dual-modal imaging system was designed and built.Using this dual-modality system,the cross-sectional high-resolution imaging of healthy humans' wrists and feet was achieved.4.First proposed and successfully measured the frequency-dependent dielectric properties changes of isolated rat blood,brain,chest muscle,heart,kidney,leg muscle,liver,lung,pancreas,and spleen tissues under low-density focused ultrasound field modulation.These data not only support the theory of the acoustoelectric effect to a certain extent but also provide a certain reference for microwave-induced thermoacoustic imaging technology and low-density focused ultrasound field neuromodulation technology which depends on the changes of dielectric properties of biological tissues.